This invention relates to signal processing apparatus and more particularly to apparatus for improving the signal-to-noise ratio of a weak signal corrupted by stronger, non-stationary or non-gaussian noise, and also for minimizing quantization word length of the digital processor.
When processing signals corrupted by additive noise with digital circuits, it is necessary to provide a sufficient level of quantization (bits of word length) to accommodate the noise or interference as well as the signal. If the noise is substantially greater than the signal, the required quantization level must be increased. As quantization levels grow, so too does the size, power, weight and cost required to perform the signal processing task. It is desirable, then, to find ways to minimize word length or quantization prior to any computationally intensive signal processing operation. This minimization process must be accomplished without significant degradation of the signal-to-noise ratio.
In addition, significant levels of interference degrade system performance by introducing errors in the desired system outputs. It is thus desirable to reduce interference level by any means possible. Such interference may be either intentional such as jamming or unintentional such as radio interference from a radio communication link.
Many methods are available to reduce interference levels. These methods all require some knowledge of the noise characteristics. One class of interference cancellers is based on knowledge of the probability law of the noise. Generally, this information includes the second moment of the noise process and possibly even complete knowledge of the noise. It is generally the case that the more that is known about the probability law of the noise, the greater the potential enhancement in signal-to-noise ratio. In some applications, the probability law of the additive noise is known and in that case, implementation of a probability domain interference canceller is straightforward. In other applications, the nature of the interference is completely unknown beforehand and measurements must be made on the noise before any enhancement in the signal-to-noise ratio or minimization of quantization is possible.
It is therefore an object of this invention to provide an interference canceller in which the probability law of a possibly non-stationary and unknown interference source is learned and to use this information to enhance signal-to-noise ratio and minimize quantization of the digital processor.
Yet another object of this invention is to provide such an interference canceller which can improve the signal to noise ratio when the noise source is zero- or non-zero-mean and non-gaussian.
Still another object of this invention is to provide such an interference canceller which is able to improve signal-to-noise ratio in real time.
A still further object of the invention is an interference canceller which can be implemented with known digital processing integrated circuits.